Alkali-free glass containing substantially no alkali metal oxides is used for various display glass substrates, etc. Further, recently, due to e.g. diversification of characteristics required for alkali-free glass, alkali-free glass with various compositions has been used, such as glass having a less B2O3 content than before.
In such alkali-free glass, silica raw material having a high melting point is used in a large amount as compared with common soda lime glass and an alkali component to facilitate melting of such silica raw material is not employed, whereby non-molten raw material is likely to remain, and uniformity of the glass composition tends to be low.
Further, a display glass substrate is required to have a high quality such that it does not have defects (such as bubbles, striae, inclusions, non-molten substances, pits, flaws, etc.) inside or on the surface of the glass substrate, which are influential over display presentation. In order not to let non-molten raw material remain inside of the glass substrate, it is considered effective to finely pulverize the raw material powder. However, if it is attempted to put fine raw material powder into a melting furnace, there will be such problems that due to scattering of the raw material powder, the glass composition tends to be unstable, and the raw material is wasted.
As a method for solving such problems, Patent Documents 1 and 2 disclose a method wherein raw material powder is granulated for use in the production of alkali-free glass.